1. Field of the Invention
The present invention relates to the purification of tertiary butyl alcohol and especially to the separation of minor amounts of close boiling oxygenated impurities therefrom by contacting the impure tertiary butyl alcohol with a large pore zeolite such as 13X zeolite in the sodium form.
2. Description of the Prior Art
Generally tertiary butyl alcohol as produced by oxidation processes such as the Oxirane Process contains small but significant amounts of impurities including water, isopropanol, acetone, methyl ethyl ketone, isobutanal formate esters, secondary butyl alcohol and the like. In certain applications the presence of such impurities causes problems with respect to the desired use. It is desirable to provide a process by which the impurities can be conveniently separated.
It is known that the close boiling oxygenated impurities can be separated to a significant degree from tertiary butyl alcohol by an elaborate and extensive distillation procedure. See U.S. Pat. No. 4,239,926. However, such procedures are costly and time consuming, involving as they do substantial capitol investments and utilities expenses.
U.S. Pat. No. 4,543,432 shows the separation of isopropanol form a tertiary butyl alcohol process stream by absorption in an asymmetric carbonacems absorbent such as Ambersorb(copyright) XE-347. Data are presented in Table II giving the equilibrium capacity of isopropanol on various adsorbents for a synthic solution of isopropanol in tertiary butanol. Data for Type JA and 13X molecular sieves are given indicating that Type JA has a slightly higher equilibrium capacity than Type 13X. Additional data relative to Type JA are given in Table IV.
It is desirable to have a simplified procedure whereby tertiary butyl alcohol process streams can be conveniently treated to separate close boiling impurities by a relatively simple and straight forward procedure.
In accordance with the present invention, a tertiary butyl alcohol process stream containing minor amounts of the impurities which are normally associated with the tertiary butyl alcohol, is contacted in the liquid phase with a large pore zeolite such as 13X zeolite or zeolite Y in the sodium form. As a result of this contact, impurities are retained on the zeolite and are thus removed or separated from the tertiary butyl alcohol; product tertiary butyl alcohol reduced in the content of contaminating impurities is readily recovered. It is generally advantageous to operate with a plurality of contact zones since the contact material must be regenerated from time to time as it loses its effectiveness for impurities removal over extended use. With a plurality of treatment zones, tertiary butyl alcohol can be treated in one zone while a separate zone is being regenerated.
Tertiary butyl alcohol as produced commercially, for example by the Oxirane Process, contains small but significant amounts of impurities, e.g. 0.1 to about 2.0 wt %. Illustrative of such impurities are water, isopropanol, acetone, methyl ethyl ketone, isobutanol, formate esters, and secondary butyl alcohol. The tertiary butyl alcohol stream to be treated illustratively comprises by weight about 10 ppm to 2% of each of the above impurities, usually about 20 ppm to 1% of each. Other materials which can readily be separated as by distillation such as methanol and methyl tertiary butyl ether may also be present. In accordance with the present invention, the impure tertiary butyl alcohol in the liquid phase is contacted with solid sodium form large pore zeolite such as 13X zeolite whereby impurities are retained on the contact zeolite solid and a liquid product tertiary butyl alcohol reduced in impurities content is conveniently separated. The contact takes place at moderate temperatures, illustratively 0 to 150xc2x0 C., although temperature is not critical. The contact solid retains the impurities adsorbed thereon and purified tertiary butyl alcohol can be separated. Initially, there can be substantially complete removal of the impurities and the recovered tertiary butyl alcohol is of exceptional purity. Over the course of time the contact solid gradually becomes less effective for the removal of these components. In accordance with the present invention at a pre-determined time when the separation efficiency has fallen below a desired point, the solid contact material is effectively regenerated, as by contact with a heated vapor stream such as nitrogen or air at a temperature of at least 3000 or by wash with a solvent such as methanol or water. It is advantageous to employ a plurality of parallel contact zones such that while one zone is being regenerated the feed is passed through a zone containing fresh or regenerated contact material so that optimum impurities removal can be achieved.
The zeolitic contact materials used in the present invention are those of large pore diameter (10 Angstroms) illustrated by 13X or zeolite Y.
The large pore zeolites are useful for the removal of essentially all of the impurities as above described, which are normally associated with tertiary butyl alcohol process streams.
A critical feature of the present invention is that the large pore zeolite be in the sodium form rather than the acid form in order to provide effective impurities removal.